The present invention relates to a sealing device in which two seals are combined with each other and into which a magnetic sensor and pulser ring to be used as a rotation detector are incorporated.
In the case of applying the above sealing device to a rolling bearing, the magnetic sensor is attached to a seal ring which is attached to a bearing ring on the stationary side, and the pulser ring is attached to a seal ring which is attached to a bearing ring on the rotary side. After a piece of rubber containing magnetic powder has been bonded to the seal ring attached to the bearing ring on the rotary side, N-poles and S-poles are alternately magnetized in the circumferential direction. Concerning this constitution, refer to JP-A-10-132603.
In the above example, since the pulser ring is directly bonded to the seal ring, the pulser ring is affected by a centrifugal force of rotation and swung in the radial direction. Accordingly, there is a possibility that an interval between the pulser ring and the magnetic sensor, which are opposed to each other, fluctuates in the radial direction.
The official gazette of JP-A-10-160744 discloses a sealing device referred to as a pack seal in which two seal rings are combined with each other. Either of these seal rings is composed in such a manner that a lip made of rubber is bonded to a metallic ring. In the case where the rolling bearing is of the inner ring rotation type, the magnetic sensor is attached to the first seal ring attached to an outer ring which is not rotated, and the pulser ring is attached to the second seal ring attached to an inner ring which is rotated.
In the above conventional example, the metallic ring is interposed between the magnetic sensor face and the pulser ring face which are opposed to each other. Due to this structure, it is impossible to reduce an interval between them exceeding a predetermined limit. Further, when lines of magnetic force generated by the pulser ring penetrate the metallic ring, an eddy current is generated. This eddy current may affect a detecting action of the magnetic sensor. Therefore, in order to further enhance the detecting accuracy of the magnetic sensor, the above structure leaves room for improvements.
The official gazette of JP-A-2001-21576 discloses a device in which the seal device is applied to a rolling bearing of the inner ring rotation type. The magnetic sensor is attached to one end face of the outer ring which is not rotated, and the magnetic ring is attached to one end face of the inner ring, which is rotated, via a support member. The support member is provided with a cylindrical portion and a flange portion extending inward in the radial direction. The magnetic ring is bonded to an outer circumferential face of the cylindrical portion of this support member. The magnetic ring is made of rubber containing magnetic powder, and N-poles and S-poles are alternately magnetized in the circumferential direction. A detection face of the magnetic sensor is perpendicular to a face to be detected of the magnetic ring.
In the above conventional example, since the detection face of the magnetic sensor is perpendicular to the face to be detected of the magnetic ring, when the position of the magnetic sensor and that of the magnetic ring are shifted from each other in the axial direction, a distance between the detecting face of the magnetic sensor and the face to be detected of the magnetic ring is extended. Therefore, it is necessary to increase the size of the piece of rubber containing magnetic powder so as to increase an intensity of the magnetic force. Further, it is necessary to employ a more sensitive magnetic sensor. Accordingly, the size of the rotation detector is increased and the manufacturing cost is raised.
The official gazette of the French Patent Publication No. FR2 574 501-A1 discloses a device in which a sealing device is applied to a rolling bearing. A magnetic sensor is attached to a seal ring attached to a bearing ring on the stationary side, and a pulser ring is attached to a seal ring attached to a bearing ring on the rotary side. In this case, the pulser ring is made of rubber containing magnetic powder and magnetized. One portion of the pulser ring comes into contact with a seal portion made of rubber provided in the seal ring and composes a portion of a tightly sealing portion for tightly sealing the inside of the bearing.
In the above conventional example, one portion of the pulser ring slidably coming into contact with the seal portion is made of rubber containing magnetic powder. Therefore, the magnetic powder acts as grinding particles, which cause abrasion in the opponent (the sealing portion on the stationary side) coming into contact with the pulser ring.